Labour's return to office after 13 years of Conservative rule left civil servants as suspicious about their new masters as the politicians were about Whitehall, the newly-opened files reveal.

On 30 October, just after Labour narrowly won the election, Derek Mitchell, private secretary at Downing Street, sent a memo to the Prime Minister, Harold Wilson, on the eve of the first Labour Budget, giving a message that highlighted the new Government's inexperience: "Warn Cabinet against leaking." Only three of the new Cabinet had served as ministers before.

Mr Wilson's inexperience of office and suspicion of the civil service, or his colleagues, led him, after a month as Prime Minister, to demand to see every document from every important meeting.

Mr Mitchell sent him a memorandum on 29 October 1964 saying: "We make a point of course of receiving and scanning papers of all Ministerial Cabinet Committees . . . It would be helpful to know how many you would like to see yourself.

"Are you content that we should pull out ones which are important, or would you like us to show to you all papers of certain committees?"

The Prime Minister scribbled his reply at the top of the memorandum: "Certainly Economic Development. I think all the others for the time being 'til I get clear which are important."